The presence of oxygen as a major impurity in grown silicon is well known. The oxygen in Czochralski (CZ) grown silicon, for example, is normally present in an amount greatly exceeding the room temperature solubility limit. Thus, it is incorporated into the CZ silicon lattice in various aggregated forms, i.e. precipitates or complexes of oxygen and silicon. The effect of the various forms of noninterstitial oxygen on the properties of silicon is complex. Some of the noninterstitial oxygen, thought to be incorporated as complexes, is known to improve the mechanical strength of silicon wafers which increases wafer resistance to warpage. Other noninterstitial oxygen, thought to be incorporated in CZ silicon as precipitates can introduce dislocations and reduce the mechanical strength of the silicon. Furthermore, precipitates of this type associated with stacking faults in the region of the semiconductor device (the substrate surface region) are detrimental to electrical performance. However, these same defects can improve electrical performance if, as gettering sites, the oxygen related defects are outside the device region, i.e. in the interior of the silicon wafer.
Gettering by oxygen precipitates is a widely used procedure for which, in each device fabrication procedure, an optimum size, concentration and spatial distribution of oxygen precipitates exists. The generation of the gettering precipitates, i.e. the precipitation kinetics of oxygen in silicon, depends on the concentration of the interstitial oxygen, carbon and, as has been shown indirectly, on the amount of initially precipitated oxygen in as-grown wafers.
Thus, to achieve reproducible oxygen precipitation during device fabrication, the amount of oxygen in precipitates and complexes in the virgin wafers should be measured in addition to monitoring carbon and interstitial oxygen concentration.
Techniques for determining the oxygen content of semiconductor materials such as silicon are well known. Some of them are destructive to the material to be analyzed and others are not. One example is by irradiation of the silicon as by He.sup.3 ions to cause a nuclear reaction with oxygen that can be used to determine oxygen content by measuring the decay product. Another example is the flame fusion technique by which the silicon is evaporated and by emission spectroscopy one can determine the oxygen content in the silicon that has been evaporated. Still another example is known as the secondary ion mass spectroscopy technique. Another technique for determining oxygen content is what may be termed wet chemical analysis by which the silicon is dissolved in a chemical which causes disassociation of the silicon and other material contents causing oxygen to be separated from the other materials. By calorimetric techniques one can determine the oxygen that was present in the material prior to the solution melt that was developed.
In all of the known techniques outlined above, the accuracy and sensitivity of the measurements are not all that is desired. Moreover, those techniques which cause destruction of the material are obviously not desirable with certain IC processing. Furthermore, most of these techniques require certain kinds of equipment and procedures that are cumbersome and difficult to utilize in conventional IC processing facilities.
In the art of IC processing, particularly using silicon material, it is known how to determine the oxygen content existing in one or more forms of oxygen. For example, the techiques for determining oxygen in interstitial positions within the crystalline lattice structure is well known as described in the ASTM Standards, Part 43-Electronics, published by the American Society for Testing and Materials, the Standard Designation:F 120-75, entitled "Infrared Absorption Analysis of Impurities in Single Crystal Semiconductor Materials," and ANSI/ASTM F 121-79, entitled "Standard Test Method for Interstitial Atomic Oxygen Content of Silicon by Infrared Absorption." Reference is made to the article cited on page 2 of the latter test method by W. Kaiser and P. H. Keck, entitled "Oxygen Content of Silicon Single Crystals," published in the J. of Appl. Physics, Vol. 28, 1957, p. 882, for a more detailed explanation of the method of the ASTM Standards.
Moreover, it is known how to determine some forms of precipitated oxygen in silicon crystals as described, for example, by S. M. Hu in the J. of Appl. Physics, 51 (11), November 1980, pp. 8945-5948. See also the paper entitled "Precipitation of Oxygen in Dislocation-Free Silicon" by K. Tempelhoff, et al., Physica Status Solidi, (a) 56, 213, (1979), pp. 213-223 for a description of additional absorption bands related to absorption by oxygen precipitates. Also see "Optical Properties of Oxygen in Silicon" by Ryzhkova, et al., Sov. Phys. Semicond., Vol. 11, No. 6, June 1977, pp. 628-630 for a description of studies of heat treatment effects of silicon on the absorption spectra of oxygen.
Furthermore, techniques are known for determining substitutional oxygen in silicon as described in a paper entitled "ACTIVATION OF THE OXYGEN DONOR IN Si ON A MICROSCALE," by P. Rava, H. C. Gatos and J. Lagowski, published in Semiconductor Silicon, 1981, The Electrochemical Society Inc. (Softbound Conference Series) (1981), pp. 232-243. However, there is nothing in the prior art known to us that teaches or suggests how to determine forms of oxygen precipitates or complexes other than that described above by S. M. Hu or Ryzhkova, et al.
It is clear that there is nothing in the art that teaches a simple, nondestructive technique that is both accurate and sensitive to determine the total oxygen content in semiconductor material.